Sample records for intermediates reaction
from WorldWideScience.org

Sample records 1 - 13 shown.



1

Reação de Baylis-Hillman: uma estratégia para a preparação de intermediários multifuncionalizados para síntese orgânica/ The Baylis-Hillman reaction: a strategy for the preparation of multifunctionalised intermediates for organic synthesis

Coelho, Fernando; Almeida, Wanda P.
2000-02-01

Resumo em inglês The Baylis-Hillman reaction has significantly advanced in the last ten years as demonstrated by a number of applications described in the literature. In this report we show some aspects of this reaction, including scope, limitations and perspectives.

Scientific Electronic Library Online (Portuguese)

2

Revisão sobre óxido nítrico/ Nitric oxide revision

Dusse, Luci Maria Sant'Ana; Vieira, Lauro Mello; Carvalho, Maria das Graças
2003-01-01

Resumo em português O óxido nítrico (NO) é um radical livre, gasoso, inorgânico, incolor, que possui sete elétrons do nitrogênio e oito do oxigênio, tendo um elétron desemparelhado. Até meados da década de 1980, o NO era considerado apenas membro de uma família de poluentes ambientais indesejáveis e carcinógenos potenciais. Atualmente, o NO constitui um dos mais importantes mediadores de processos intra e extracelulares. Este radical é produzido a partir da L-arginina, por uma (mais) reação mediada pela enzima NO-sintase constitutiva (c-NOS) e induzível (i-NOS). O NO apresenta um papel dúbio, às vezes benéfico, outras vezes prejudicial ao organismo. Está envolvido no relaxamento vascular e tem um papel de grande importância na proteção do vaso sangüíneo. Constitui um importante mediador citotóxico de células imunes efetoras ativadas, capaz de destruir patógenos e células tumorais. Possui, ainda, um papel como mensageiro/modulador em diversos processos biológicos essenciais. No entanto o NO é potencialmente tóxico. A toxicidade se faz presente particularmente em situações de estresse oxidativo, geração de intermediários do oxigênio e deficiência do sistema antioxidante. A determinação laboratorial do NO é complexa, e a caracterização de ativadores e inibidores específicos da síntese de NO constitui o novo desafio para o entendimento e o tratamento de várias doenças. Estudos envolvendo o NO têm sido um dos principais alvos da indústria farmacêutica. Resumo em inglês Nitric oxide (NO) is an inorganic and incolor free radical gas containing seven electrons from nitrogen and eigth from oxigen and one unpaired electron. Until midlle of 1980 decade, NO was considered as a member of an undesiderable and envirommental poluents family and as a potential carcinogen agents. At the moment, NO constitutes one of the most important mediators of intra and extra cellular processes. This radical is produced from the L-arginine envolving a reaction m (mais) ediated by constitutive and inducible NO synthase. NO presents a dubious role, sometimes it brings benefits, sometimes it is harmful. It is envolved in the vascular relaxing and it protects the blood vessels. It constitutes an important cytotoxic mediator on immune activated cells capable of killing pathogenic agents and tumor cells. It also has a role as messager/modulator in a variety of essential biological processes. However, NO is a potentially toxic agent, whose toxicity could be particulary denoted in stress oxidative conditions, by the generation of O2 intermediates and antioxidant system deficiency. Laboratory measurement of NO is complex and the characterization of specific activators and inhibitors of the NO synthesis constitutes the new challenge for a better comprehension and treatment of a number of pathologies. NO studies have been one of the main target for pharmaceutical industries.

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3

Utilização de α,α-Diclorociclobutanonas em Síntese de Produtos Naturais/ The utilization of α, α-dichlorocyclobutanones in the synthesis of natural products

Lima, Marco Edilson F. de; Coelho, Fernando A. S.
1997-06-01

Resumo em inglês The preparation and chemical potentiality of a,a-dichlorocyclobutanones as useful intermediates in the total synthesis of natural products are reviewed. Some aspects related to the recent advances reported in the literature about the mechanism of [2+2] cycloaddition reaction between dichloroketene and olefins are also presented.

Scientific Electronic Library Online (Portuguese)

4

Redução de amidas por boranos/ Reduction of amides by boranes

Alcântara, Antônio Flávio de Carvalho; Barroso, Hiléia dos Santos; Piló-Veloso, Dorila
2002-05-01

Resumo em inglês Despite the fact that boranes are frequently used in amide reductions, the reaction mechanisms of the involved are note well known. This work presents the results of a bibliographic search on probable amide reduction mechanisms and an analysis of the existing literature. Steric and electronic effects were considered in light of reactivity since it could be concluded that the formation of intermediates and products depends mainly on the substitution patterns of both the bo (mais) ron and nitrogen atoms. Otherwise, results described in the literature for the reactions of boranes, sodium borohydride, lithium aluminum hydride, alkylboranes or haloboranes with others functional groups such as carboxylic acids, esters, ketones and alkenes were analysed with the aim to obtain something about the N-substituted amide reactions employing boranes.

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5

Reações orgânicas em meio aquoso/ Organic reactions in aqueous media

Silva, Flavia Martins da; Jones Jr, Joel
2001-10-01

Resumo em inglês The use of water as solvent in organic reactions has been uncommon for several reasons, among them the low solubility of the reactants, the incompatibility of the intermediates with water, and the competition between the desired reaction and hydrolysis. Breslow in 1980, demonstrated that the hydrophobic effect accelerates Diels-Alder reactions and gives a high endo/exo selectivity. Since then, many other reactions were studied in this medium, and below we show the princip (mais) al results. Besides the academic interest, human and economic aspects are included in this study. Water as a solvent minimizes environmental impact, costs and increases operational safety.

Scientific Electronic Library Online (Portuguese)

6

Reações de inserção intramolecular de diazo compostos polifuncionais catalisadas por ródio(II): síntese de oxetan-3-ona-2-carboxilato e outros heterociclos funcionalizados/ Rhodium(II)-catalysed intramolecular insertion reaction of multifunctional diazo compounds: synthesis of oxetan-3-one-2-carboxilate and other heterocycles

Padwa, Albert; Sá, Marcus Mandolesi
1999-12-01

Resumo em inglês gamma-Hydroxy-alpha-diazo-beta-ketoesters are key intermediates in the chemistry of penicilin-based antibiotics and natural products. The method developed here for the synthesis of ethyl 2-diazo-4-hydroxy-3-oxo-butanoate 17 (in two steps from the diazo mercurial 2) compares very favorably with those reported in the literature for similar compounds. The Rh2(OAc)4-mediated intramolecular OH-insertion reaction of the diazo hydroxy ester 17 was investigated, furnishing the ox (mais) etan-3-one-2-carboxilate 18 in good yield. When the diazo ester lacks a free hydroxyl group as in the case of the phenoxy diazo ester 11 an intramolecular CH-insertion takes place, affording the 2H-chromene 20 in almost quantitative yield. The behavior of other functionalized diazo esters towards Rh2(OAc)4 was also investigated.

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7

Isolamento e caracterização de acil-tiossemicarbazidas como intermediários na síntese de compostos mesoiônicos/ Isolation and characterization of acyl-thiosemicarbazides as intermediates in mesoionic compounds synthesis

Maciel, M. A. M.; Echevarria, A.; Rumjanek, V. M.
1998-10-01

Resumo em inglês 1,3,4-thiadiazolium-2-aminides and their isomers 1,3,4-triazolium-2-thiolates have been synthesized via anhydroacylation reactions. This work presents a study by infrared monitoring of the reaction between substituted aroyl acid chlorides and 1,4-diphenylthiosemcarbazide. The intermediates and products were isolated, purified and charaterized by IR and 13C NMR spectroscopy. The increasing or decreasing in intensity of characteristic stretching bands indicated the rate dep (mais) endence on the electronic nature of substituents. The results also demonstrate that 1,3,4-triazolium-2-thiolates are obtained in anhydrous conditions whereas presence of water leads to a mixture of the isomers.

Scientific Electronic Library Online (Portuguese)

8

Influência das variáveis de processo na alcoólise enzimática de óleo de mamona/ Evaluation of the influence of process variables on enzimatic alcoholysis of castor oil

Oliveira, D.; Oliveira, J.V.; Faccio, C.; Menoncin, S.; Amroginski, C.
2004-06-01

Resumo em português O potencial de aplicação de lipases em processos biotecnológicos para a modificação de óleos e gorduras tem sido objeto de grande interesse nos meios científico, econômico e industrial nos últimos anos. Além da atividade de hidrólise de ésteres, as lipases podem catalisar uma grande variedade de reações de esterificação, transesterificação e poliesterificação. A transesterificação inclui acidólise, interesterificação e alcoólise. Neste trabalho r (mais) eações de alcoólise de óleo de mamona para produção de ésteres de ácidos graxos foram estudadas devido a sua importância na obtenção de, por exemplo, agentes de antifricção, emulsificantes, intermediários para produzir uma numerosa quantidade de oleoquímicos e combustível alternativo ao diesel e/ou aditivo ao diesel de petróleo (biodiesel). Neste contexto, foi estudada a etanólise enzimática de óleo de mamona com lipase comercial (Lipozyme IM) usando n-hexano como solvente. Os experimentos foram realizados variando a temperatura, as concentrações de água e enzima no meio reacional e a razão molar óleo-etanol, de acordo com um planejamento de experimentos pré-estabelecidos. Um modelo empírico foi utilizado para avaliar a influência das variáveis de processo no rendimento e, desta forma, as condições de operação que maximizam a produção de ésteres foram estabelecidas para a enzima utilizada. Resumo em inglês The use of lipases as biocatalysts in ester synthesis has been the object of growing interest. In addition to glycerol ester hydrolysis, lipases can catalyze a wide variety of esterification, transesterification and polyesterification reactions. The transesterification includes acidolysis, interesterification and alcoholysis. We consider in this report the application of lipases in the alcoholysis of brazilian vegetable oil in the production of fatty acid esters due to it (mais) s importance as, for example, antifriction agents, food preservatives, emulsifiers and intermediates to produce a number of oleochemicals and fuel alternatives (biodiesel). In this work, enzymatic alcoholysis of castor bean oil with an immobilized lipase (Lipozyme IM) was accomplished using n-hexane as solvent. In order to maximize the esters production a Taguchi design was adopted varying temperature, water and enzyme concentrations in the reaction media and the oil:ethanol molar ratio. The reactions were monitorated by determining the glycerol production. An empirical model was built to evaluate the influence of the process variables on the conversion and afterwards the operating conditions that maximize esters production were established.

Scientific Electronic Library Online (Portuguese)

9

Formação de adutos exocíclicos com bases de DNA: implicações em mutagênese e carcinogênese/ Exocyclic DNA adducts: implications in mutagenesis and carcinogenesis

Loureiro, Ana Paula M.; Di Mascio, Paolo; Medeiros, Marisa H. G.
2002-09-01

Resumo em inglês A number of ring-extended DNA adducts resulting from reaction of alpha,beta-unsaturated aldehydes, or their epoxides, with DNA bases have been characterized in recent years. These adducts can lead to miscoding during DNA replication which, if not repaired, result in mutations that can contribute to cancer development. Recently, the use of ultrasensitive methods allowed the detection of background levels of etheno DNA adducts in tissues of untreated animals and humans sugg (mais) esting the existence of endogenous sources of reactive intermediates. In this review, we briefly summarize the recent advances in the chemistry of these DNA lesions.

Scientific Electronic Library Online (Portuguese)

10

Degradação de BTXs via processos oxidativos avançados/ Degradation of BTXs by advanced oxidative processes

Tiburtius, Elaine Regina Lopes; Peralta-Zamora, Patricio; Emmel, Alexandre; Leal, Elenise Sauer
2005-02-01

Resumo em inglês In this study the efficiency of advanced oxidative processes (AOPs) were investigated toward the degradation of aqueous solutions containing benzene, toluene and xylenes (BTX). The results indicated that BTX can be effectively oxidized by the UV-A-assisted photo-Fenton process. The treatment permits almost total degradation of BTX and removal of more than 80% of the phenolyc intermediates at reaction times of about 30 min. Preliminary investigations using solar light sugg (mais) est a good potentiality of the process for the treatment of large volumes of aqueous samples containing these polluting species.

Scientific Electronic Library Online (Portuguese)

11

Contribuições recentes da reação de hidroformilação na síntese de produtos farmacêuticos: parte II/ Current improvement to the synthesis of pharmaceuticals by hydrofor-mylation reaction: part II

Botteghi, Carlo; Marchetti, Mauro; Del Ponte, Gino
1997-02-01

Resumo em inglês The hydroformylation reaction represents one of the most important C1-chemistry area in the chemical industry. This catalytic process, which has been developed up to now mainly to the production of commodities chemicals, has shown a remarkable potential for the preparation of several categories of specialty chemicals and in particular pharmaceutical compounds. Arylpropanoic acids, various amines containing aryl groups, and intermediates for the preparation of vitamins, ca (mais) rbocyclic and heterocyclic compounds and many other classes of organic molecules endowed with pharmacological activity are currently accessible in good-to-high yields through hydroformylation of selected olefinic substrates. The asymmetric hydroformylation is going to reach the stage of maturity and hence to contribute in solving many troublesome synthetic problems connected with the preparation of pharmacologically active compounds with very high enantiomeric purity. The present survey emphasizes the usefulness of synthesis gas as a starting material in fine chemistry, which is expected to be important for industry.

Scientific Electronic Library Online (Portuguese)

12

Atividade farmacológica da monocrotalina isolada de plantas do gênero Crotalaria/ Pharmacological activity of monocrotalina isolated from plants of the genus Crotalaria

Honório Júnior, José E. R.; Soares, Paula M.; Melo, Célio L. de; Arruda Filho, Antônio C. V.; Sena Filho, José G.; Barbosa Filho, José M.; Sousa, Francisca Cléa Florenço; Fonteles, Marta Maria França; Leal, Luzia Kalyne de Almeida; Queiroz, Maria Goretti Rodrigues de; Vasconcêlos, Silvânia M.M.
2010-07-01

Resumo em português Crotalaria retusa é uma planta encontrada no Nordeste brasileiro, pertence ao gênero Crotalaria e à família Leguminosae, e possuem mais de seissentas espécies no mundo e mais de quarenta no Brasil. As variedades tóxicas mais conhecidas são C. spectabilis, C. crispata, C. retusa, C. dura e C. globifera. Plantas do gênero Crotalaria são de interesse porque são usadas na medicina popular. Esses gêneros são ricos em alcaloides pirrolizidínicos (AP), que são as p (mais) rincipais toxinas e apresentam efeitos pneumotóxicos, nefrotóxicos, cardiotóxicos, fetotóxicos, carcinogênicos, inflamação, hemorragia e fibrose. A monocrotalina é o principal alcaloide pirrolizidínico encontrado nessas plantas e é ativamente oxidada in vivo pelo citocromo P450 no fígado, formando intermediários altamente reativos tipo pirrólicos que são responsáveis pela ligação cruzada do DNA-DNA e DNA-proteína. O presente trabalho teve como objetivo fazer um levantamento bibliográfico via internet, utilizando bancos de dados, programas de pesquisa científica e pesquisa em livros relacionados, acerca da atividade farmacológica e do mecanismo de ação da monocrotalina extraída de plantas do gênero Crotalaria, ressaltando desde os aspectos botânicos da planta, estrutura química dos alcaloides pirrolizidínicos, exemplos experimentais de toxicidade e provável mecanismo de ação. Resumo em inglês Crotalia retusa is a plant found in Brazilian Northeast and belongs to the genus Crotalaria and the family Leguminosae, which comprises more than 600 species throughout the world and more than forty in Brazil. The most known toxic species are C. spectabilis, C. crispata, C. retusa, C. dura and C. globifera. Plants of the Crotalaria genus are of great interest because they are used by humans for folk medicine. These plants are rich in pyrrolizidine alkaloids (PA), which ar (mais) e the main toxins that cause effects such as pneumotoxic, nefrotoxic, cardiotoxic, fetotoxic, carcinogenic, inflammation, hemorrhage and fibrosis. Monocrotaline is the main pirrolizidinic alkaloid found in plants and is actively oxidated in vivo by the cytochrome P450 in the liver, yielding highly reactive pyrrolic type intermediates, which are responsible for DNA-DNA and DNA-protein cross-links reaction. The aim of this work is to make a bibliographic survey via internet, using databases, scientific research programs and related books, about pharmacological activity and mechanism of action of monocrotaline extracted from plants of Crotalaria genus, emphasizing plant botanical aspects, chemical structure of pirrolizidinic alkaloid, experimental examples of toxicity and probable action mechanism.

Scientific Electronic Library Online (Portuguese)

13

Acilação de Friedel-Crafts do 2-metoxinaftaleno usando o ácido dodecafosfotúngstico suportado em sílica (HPW/SiO2) como catalisador e acetonitrila como solvente/ Friedel-Crafts acylation of the 2-methoxynaphthalene using the silica-supported dodecatungstophosphoric acid (HPW/SiO2) as catalyst and acetonitrile as solvent

Santos, Gil Luciano Guedes dos; Silva, Creuza Souza; Cardoso, Luiz Augusto Martins
2010-01-01

Resumo em inglês The synthesis of fine chemicals intermediates using Friedel-Crafts acylation is one of the most important methods in chemical technology. In this work, the acylation of 2-methoxynaphthalene with acetic anhydride using a silica-supported dodecatungstophosphoric acid catalyst (HPW/SiO2) and acetonitrila as solvent was studied, showing that this reaction is a feasible alternative to produce intermediaries to replace the current methods of production. The reactions using acet (mais) onitrile solvent showed yields greater than or equal to the reactions using traditional solvents such as nitrobenzene and dichloroethane. Finally, the modified Eley-Rideal mechanism was proposed to elucidate the experimental data obtained.

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